Investigation of the Foam Development Stages by Non-Destructive Testing Technology Using the Freeze Foaming Process

Abstract

With a novel Freeze Foaming method, it is possible to manufacture porous cellular components whose structure and composition also enables them for application as artificial bones, among others. To tune the foam properties to our needs, we have to understand the principles of the foaming process and how the relevant process parameters and the foam’s structure are linked. Using in situ analysis methods, like X-ray microcomputed tomography (µCT), the foam structure and its development can be observed and correlated to its properties. For this purpose, a device was designed at the Institute of Lightweight Engineering and Polymer Technology (ILK). Due to varying suspension temperature and the rate of pressure decrease it was possible to analyze the foam’s developmental stages for the first time. After successfully identifying the mechanism of foam creation and cell structure formation, process routes for tailored foams can be developed in future.

Tailoring of Hierarchical Porous Freeze Foam Structures

“…With current methods, material states can only be analyzed either before or after a change in the material [27,28]. An in-situ freeze foaming examination device, to be used inside a V|TOME|X L450 (General Electric, Cincinnati, OH, USA), was developed during former research activities, to investigate the freeze foaming during the process [25]. For the present experimental study, a modification of the developed in-situ CT device was required to ensure a quicker response of the vacuum system as well as an increase in either contrast or resolution [25].…”

“…An in-situ freeze foaming examination device, to be used inside a V|TOME|X L450 (General Electric, Cincinnati, OH, USA), was developed during former research activities, to investigate the freeze foaming during the process [25]. For the present experimental study, a modification of the developed in-situ CT device was required to ensure a quicker response of the vacuum system as well as an increase in either contrast or resolution [25]. The volume of the recipient being evacuated was decreased and an additional cold trap was installed.…”

“…Two types of scans were performed: After filling molds with the model suspension (11.00 g; filling level 1/3), the freeze foaming process was started and recorded without rotation as a sequence of 2D radiographic images to observe the formation and coalescence of pores and measure the foaming speed as well as the final height. This was achieved by pixel tracking of the single images with the software IMAGEJ, as further described by Maier et al [25].…”

“…In the initial investigation, it was possible to gain a deeper understanding of the principal mechanisms relating to the formation of freeze structures by carrying out analyses of the influence of selected suspension and process parameters on the resulting structural properties of biocompatible ceramic foams [22][23][24][25]. With the help of modern methods of non-destructive material testing, a first-time phenomenological investigation and foam structure analysis during the foaming process could be carried out by using in-situ X-ray radiography.…”

Investigation of Targeted Process Control for Adjusting the Macrostructure of Freeze Foams Using In Situ Computed Tomography

“…The in situ investigation of the foaming process of ceramic foams with a systematic interaction between the suspension composition and process control has not been presented thus far. To examine the targeted process control for adjusting the macrostructure of freeze foams, a customized in situ system for CT investigations was developed in [19]. With this device, more precise and adjustable process control were possible in contrast to commercial freeze dryers.…”